Transfer line and valve assembly combination for handling molten liquids

ABSTRACT

Disclosed herein is an electrically-heated transfer line and valve assembly combination which is particularly adapted for transferring molten metals from one point to another. The valve assembly is basically a cylindrical valve body having a slidable stem therein, with the stem being moved between open and closed positions by mechanical power, such as an air cylinder or hydraulic cylinder. In the apparatus described herein the transfer line and valve assembly form a part of the same electrical circuit, the objective being to achieve uniform heating throughout the entire transfer system. Specific applications of the valve assembly include its use as an end valve on a transfer line in die casting or permanent mold casting, and as a metering valve in cold chamber die casting of magnesium alloys.

11] 3,72fifi [451 Apr. 10, 1973 3,556,360 1/1971 Stelson 137/2403,651,825 3/1972 Sury...... ..............................137/240 N novn m mm 0 we mm M Mm TA m HANDLING MOLTEN LIQUIDS [75] Inventors:Stephen C. Erickson; Foster C.

FOREIGN PATENTS OR APPLICATIONS ma ct e am a my 4M mm mm Pm W m n c m hh .m wM ma m m %M w m n A M U [57 7 ABSTRACT Disclosed herein is anelectrically-heated transfer line and valve assembly combination whichis particularl adapted for transferring molten metals from one poi [22]Filed; Nov. 26, 1971 [21] Appl. No.: 202,150

[52] US. 137/240 to anothen The valve assembly is basically a cylindri e0 re cal valve body having a slidable stem therein, with the stem beingmoved between open and closed positions References Cited UNITED STATESPATENTS by mechanical power, such as an air cylinder or hydrauliccylinder. In the apparatus described herein the transfer line and valveassembly form a part of the same electrical circuit, the objective beingto achieve uniform heating throughout the entire transfer systemSpecific applications of the valve assembly include its use as an endvalve on a transfer line in die casting or ...25l/290 permanent moldcasting, and as a metering valve in cold chamber die casting ofmagnesium alloys.

5 Claims, 2 Drawing Figures PATEHTEU APR 1 5 SHEET 1 BF 2 INVENTORS. 6.[H045 on /6r 6. (Senna/f HGEN T PATENTED APR 1 0 I975 SHEET 2 0F 2INVENTORS. S/cphen Cfric/rson F05 fer C. Benn e BY j mm a

HGENT TRANSFER LINE AND VALVE ASSEMBLY COMBINATION FOR HANDLING MDL'IENLIQUIDS BACKGROUND OF THE INVENTION In a typical cold chamber processfor die casting light metals, such as magnesiumalloys, the molten metalto be die cast is held in a suitable vessel, such as a crucible ormelting pot. In one of the conventional magnesium alloy die castingprocedures, the molten metal is transferred from the holding vessel tothe shot well of the die casting machine through a heatedtransfer line,which includes a metering valve at the outlet end of the transfer line.The metering valve commonly employed The apparatus utilized in' the diecasting procedure described above is not entirely satisfactory, however,because of various problems encountered in the operation of the meteringvalve. For example, in order to successfully transfer the molten metalfrom the holding vessel to the shot well, the transfer line and meteringvalve must be kept heated to atemperature above the melting point of themetal. Usually, the transfer line and valve are heated by enclosingthese components in a gas-fired heater shroud. A primary disadvantage ofthe heater shroud, however, is that it is very difficult to heat thevalve assembly uniformly with such a heating system.

Using the heater shroud method, for example, itis difficult to heat thestem seal area, i.e., the point of sliding contact of the upper valvestem with the valve body. This is particularly'true in a valve assemblyin which a packing material is used to provide the desired liquidtightseal at the stem seal point. In this situation, therefore, if the moltenmetal in the valve body comes in contact with a cold valve stem, itwillfreeze and deposit a layer of solid metal on the stem. On the upstrokeof the stem, therefore, the frozen metal film will tear out the softerpacking material and destroy the stem seal.

One solution to the problem of stem seal damage is to allow the moltenmetal to only partially fill the valve body, i.e., so that the level ofthe molten metal is below the stem seal area. This procedure is alsoundesirable, however, in that a protective gas atmosphere must bemaintained in the unfilled portion of the valve body to prevent surfaceoxidation of the liquefied metal. Another disadvantage in this procedureis that the maximum pressure that can be exerted against the metal mustbe controlled to prevent the molten metal from rising too high in thevalve.

SUMMARY OF THE INVENTION Accordingly, a broad object of the inventionis'to provide an apparatus that is useful for transferring moltenliquids from one point to another which does .not have the drawbacks ofthe prior apparatus.

A more specific object is to provide an apparatus particularly adaptedfor transferring molten metal which comprises the combination of anelectrically heated transfer line and valve assembly, wherein the valvebody functions as a resistance element in the heating circuit.

Another object is to provide an apparatus as described in which thevalve assembly is suitable as a metering valve for a cold chamber diecastingmachine.

Another object is to provide an apparatus as described in which thevalve assembly is suitable as an end valve on a line for transferringmolten liquids.

Broadly, the invention provides an apparatus for transferring moltenliquids from one point to another. The basic apparatus comprises atransfer line for conducting the molten liquid, which includes a valveassembly connected to the outlet end of the transfer line. The valveassembly is defined generally by a valve body which includes a neckportion at the upper part of the valve body, a cone-shaped valve seat atthe lower end of the valve body and a cylindrical stem within the valvebody. The central portion of the stem is in sliding contact with theneckportion of the valve body and the upper and lower portions of thevalve body are spaced from the stem to define annular chambers above andbelow the neck portion. The lower chamber, which connects into thetransfer line, provides a reservoir for receiving molten liquid from thetransfer line. A packing material is positioned in the upper chamber toprovide a liquid-tight seal between the valve stem and valve body. I

The valve stem further includes a hemispherical lower end adapted tosealingly engage the cone-shaped valve seat and a central bore whichextends lengthwise through the stem. Communicating with the upper end ofthe stem bore is an inlet channel for directing a fluid material intothe bore. The fluid material is discharged into the valve seat throughseveral outlet channels which connect the lower end of the stem borewith the lower end of the valve stem. The upper end of the valve stem isconnected by a coupling member to a power means for moving the stern upand down in the valve body. To keep the liquid being transferred in amolten state, the transfer line and valve body are heated by a commonelectrical circuit which receives current from a source of electricalpower.

DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation view, partly insection and partly schematic, of a conventional die casting apparatuswhich includes a transfer line and valve assembly combination accordingto an embodiment of this invention.

FIG. 2 .is an enlarged detail view of the .valve assembly illustrated inFIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT including an impeller unit 15. Theimpeller unit is positioned in a metal-conducting passageway 16 which isdefined in a housing enclosing the unit. The metal inlet end of transferline 13 is connected into the metal outlet end of passageway 16 by atwo-part coupling member 17.

A valve assembly, as indicated generally by numeral 18, is connected tothe metal outlet end of transfer line 13. In a metal die castingoperation, the valve assembly 18 may provide a means for metering a shotof molten metal from transfer line 13 into the shot well 19 of the diecasting machine. The transfer line and valve assembly are electricallyheated to keep the metal 12 in a molten condition during transfer fromthe holding pot 11 to shot well 19. One side of the electrical circuitcomprises a lead 20, which connects at one end to electrode 21 mountedon transfer line 13 and at the pposite end to a transformer. The otherside of the circuit comprises a lead 22, which connects at one end to anelectrode 23 mounted on valve assembly 18, and at the opposite end tothe transformer. The transformer, in turn, is connected into a source ofpower by a lead 24.

Referring particularly to FIG. 2, the valve assembly is illustrated inenlarged detail. In general, the valve assembly 18 is defined by acylindrical valve body 25 and a cylindrical valve stem 26, which isslidable within the valve body. In the operating position of stem 26,the stem is in sliding contact with the inner wall surface of a neckportion 27, which is generally defined at the upper part of valve body25. Above neck portion 27 the inner wall surface of valve body 25 isspaced from valve stem 26 to define an upper annular chamber within thevalve body. Also, below neck portion 27, the inner wall surface of valvebody 25 is spaced from valve stem 26 to define a lower annular chamberin the valve body.

At the metal outlet end of transfer line 13,'the line connects directlyinto the lower annular chamber of valve body 25. The lower chamber ofthe valve body, therefore, provides a reservoir for receiving the moltenliquid 12 from transfer line 13. The upper annular chamber of valve body25 is filled with a packing material 28, which is compressed and held inplace by a packing gland 29. The packing material 28 provides aliquid-tight seal between the valve stem 26 and the inner wall surfaceof the valve body. The valve body 25 and transfer line 13 are covered bya conventional high temperature heat insulating material 30. Suitablepacking materials include graphite and asbestos. The preferred packingis a flexible graphite material sold under the name Graphoil. Apreferred insulating material is a stable, high temperaturealumina-silica ceramic fiber, which is sold under the name Kaowool.

The lower end of valve body 25 is defined by a coneshaped valve seat 31.The lower end of valve stem 26 defines a hemispherical tip which willwedgingly engage the valve seat 31 when the valve is in shut offposition. Extending lengthwise through valve stem 26 is a central bore32. A nipple fitting 33 is attached to the upper end of valve stem 26.The nipple fitting is in direct communication with a small crosswisebore 33a, which intersects with the upper end of lengthwise bore 32. Thefitting 33 and bore 33a, therefore, provide an inlet channel fordirecting a fluid material into bore 32.

At the lower end of bore 32, several outlet channels 34 extenddownwardly and outwardly from bore 32 and extend on through thehemispherical tip of valve stem 26. One example of the use of bore 32 isin a magnesium alloy die casting operation. In this type of operation agas, such as argon, is directed into bore 32 through the fitting 33 andbore 330 and is discharged through the outlet channels 34 into the lowerend of valve seat 31. The purpose of the gas is to provide a protectiveatmosphere which will prevent oxidation of the small amount of moltenmetal which remains in the valve seat after each shot.

The upper end 26b of valve stem 26 is connected to the lower end of apiston rod 35 by a split coupling 36. Piston 35, which moves the valvestem 26 up and down in valve body 25, is operated by a power cylinder37. Cylinder 37 is preferably a fluid power cylinder, such as an aircylinder, hydraulic cylinder, or the like. A mounting assembly forcylinder 37 is provided by a lower mounting plate 38, which is attachedto valve body 25, and an upper mounting plate 39. The mounting platesare tied together by rod supports 40 and 41.

The upper part of the left half of split coupling 36 includes an earmember 42 on which is mounted an upstanding threaded stud member 43.Similarly, the right half of split coupling 36 includes a correspondingear member 44, on which is mounted an upstanding threaded stud member45. Stud members 43 and 45 are in direct alignment with the underside ofmounting plate 39, so that the top of each stud member can bump againstplate 39 on the upstroke of valve stem 26. The stud members, therefore,function as adjustable stop members for adjusting the length of strokeof the valve stem 26.

An optional featureof the valve assembly 18 is a helical compressionspring 46, which is carried on piston stem 35 and is fitted between theunderside of mounting plate 39 and the upper face of split coupling 36.Spring 46 provides a return means for urging the valve stem 26downwardly into the seating position in valve seat 31 (shut offposition) after the upstroke is completed. An additional function of thespring is to act as a safety device. For example, in case of a suddenloss of power to cylinder 37, the spring 46 will automatically returnvalve stem 26 back to the seating position, so that the valve isimmediately shut off.

In practice, it is contemplated that the valve assembly of thisinvention may be employed in any of various applications requiringtransfer of a molten liquid from one point to another. Representative ofsuch applications are the use of the valve assembly as an end valve on apipe line for transferring molten metals, such as magnesium or zincalloys, molten salt compositions, and the like. With regard to moltenmetals, the valve assemblY is particularly adapted for handling moltenmagnesium alloys in die casting and in permanent mold castingoperations. Specific applications include use as a metering valve incold chamber die casting, as an end valve on an electrically heatedtransfer pipe, as an end valve on a pipe line used for casting ingots,and as a control valve for filling a permanent mold in a permanent moldcasting process.

To illustrate the practice of the invention, the use of the valveassembly 18 as a shot metering valve for a cold chamber machine for diecasting a magnesium alloy, will now be described. As mentionedpreviously, it is essential that certain internal areas of the valvebody be kept uniformly hot, i.e., at a temperature above the meltingpoint of the metal. In the present valve assembly there are two criticalareas in the valve body 25 which require uniform heat. One of theseareas is defined by the upper chamber around the valve stem 26, whichincludes the packing material 28. The other critical area is that partdefined by the lower chamber which contains the molten metal 12.

To keep the critical areas of the valve body heated, the apparatus isconstructed such that the valve body 25 is connected into a commonelectrical circuit which heats the transfer line and the valve assembly.For example, as shown in the drawing (note particularly FIG. 1) thevalve body 25 is connected into one side of the circuit throughelectrode 23 and lead 22, which, in turn, connects into a transformerand power source. The other side of the circuit is formed by transferline 13, which connects into the transformer and power source throughelectrode 21 and lead 20. By placing the valve body 25 directly in thecurrent path, therefore, the valve body actually functions as aresistance element in the circuit. Since the valve body does act as aresistance element, several factors must be considered in designing thevalve body. For example, the amount of electrical power required to heatthe valve body to the desired operating temperature will depend onvariables such as the physical properties of the molten liquid beinghandled, the amount and type of insulation used to cover the valve body,the material used to construct the valve body, and the cross-sectionalarea of the valve body.

Since electrical resistance heating is proportional to the effectiveresistance offered by the current conductor, it is of prime importanceto designthe valve body with a cross-sectional area which will providethe desired amount of effective resistance. The amount of alternatingcurrent power required, therefore, can be determined according to theformula P PR, in which P power, I current and R effective resistance.From this formula, therefore, it can be concluded that the amount ofheat or power dissipated can be controlled by changing either thecurrent input or by changing the amount of effective resistance offeredby the conductor.

The usual way to regulate the current input is to control the sourcevoltage. The direct current resistance offered by the conductor,however, is an inherent property of the conductor, which depends onfactors such as the resistivity of the material which comprises theconductor, the length of the conductor, and the crosssectional area ofthe conductor (the area which lies perpendicular to the direction ofcurrent flow). Resistivity is determined according to the formula R K(L/A), in which R resistance, K resistivity, L length and Across-sectional area. The effective resistance encountered withalternating current is greater due to the skin effect, eddy currents,and hysteresis losses in the metal pipe.

Based on the foregoing principles, therefore, it will be apparent thatthe resistance characteristic of the valve body can be altered inseveral ways. One way is to vary the cross-sectional area. Another wayis to change the type of material used to construct the valve body.

Understandably, the choice of materials of construction is limited tothose materials which are compatible with the molten liquid beinghandled by the valve assembly. To successfully handle molten magnesiumalloys, for example, materials of construction are limited almostexclusively to the various chrome steel compositions. The reason forthis is the highly corrosive nature of molten magnesium. Since the Kfactor (resistivity) of most steel compositions is very similar,however, it is generally considered impractical to attempt to alter theresistance characteristic of the conductor (valve body) by a change ofmaterial.

Since the area defined by the upper part of valve stem 26 and packingmaterial 28 is difficult to heat, several solutions have been proposedto alleviate the problem. One solution is to vary the cross-sectionalarea of the upper part of the valve body 25, which is achieved bydecreasing the thickness of the upper valve body wall. Another solutionis to connect the valve stem 26 into a second electrical circuit. Inthis arrangement, therefore, the valve stem, like the valve body, willfunction as a resistance element to add additional heat to the valvestem-packing area. As partly shown in FIG. 2, the second circuit isprovided by an electrical lead 47, which connects the valve stem 26 withthe power source through an electrode 48 mounted on the valve stem. Ifthe resistance of the valve stem is not sufficient to provide thedesired amount of heat, the resistance can be increased by altering thecross-sectional area of the stem.

Another factor which must be considered in the electrically-heatedtransfer system of this invention is the overall resistivity offered bythe transfer line-valve assembly combination. In other words, therelative sizes of the transfer line and valve assembly must conform tothe extent that each part of the combination has essentially the sameamount of electrical resistance per unit of length. The reason for theconformance requirement in this system is that both the transfer lineand valve assembly form a part of the same electrical circuit.

In a magnesium alloy die casting operation, small particles of extremelyhard materials, such as magnesium oxides, nitrides and inter-metalliccompounds, may

' form inside the valve body. These hard particles have a tendency towedge between the upper valve stem and valve body and the valve stem tipand valve body seat, and thereby cause excessive wear at these points.In practice, therefore, it is preferred to provide a covering layer 26aon the upper part of valve stem 26, a covering layer 26c on the valvestem tip, and an inner liner 31a in valve seat 311, which comprises anabrasion-resistant material. Suitable materials are high temperaturegrade, wear-resistant metal compositions, which are relatively inert toreaction with the aluminum component present in some magnesium alloys.Preferred materials include alloys comprising a mixture of cobalt,chromium and tungsten.

In a working embodiment of the invention, the valve body 25 wasfabricated of type 410 stainless steel and the transfer line 13 of type430 stainless steel. The length of the valve body was about 7.5 inches.The average outside diameter of the valve body above and below the neckportion 27 was about 2.67 inches. At the neck portion the averageoutside diameter was about 2.375 inches. The average inside diameter ofthe valve body was about2.0 inches above and below the neck portion 27and about 1.25 inches at the neck portion. The length of the transferline was about 3.0 feet and the inside diameter was 2.0 feet. Both thevalve body and transfer line were covered with an insulation material 30(Kaowool) having a thickness of about 2.0 inches.

In die casting a magnesium alloy, the valve body and transfer line weremaintained at an operating temperature of about l,200F. The currentrequired to maintain the operating temperature was about 1,450 amperesand the voltage was about 3.2 volts, as measured across the electricalleads 20 and 22. The power input was maintained at about 4,640 voltamperes. From past experience with the use of electrically-heated pipelines in a magnesium alloy die casting operation, it has been found thatthe power factor is usually about 0.75 in a set up similar to thatdescribed above. For this reason the power input was estimated to beabout 4,640 X 0.75, or 3,480 watts.

What is claimed is:

1. In an apparatus for transferring a molten liquid from one point toanother, the combination which includes:

a. a transfer line for conducting the molten liquid, in-

cluding a valve assembly connected to the outlet end of the transferline,

b. the valve assembly being defined by a cylindrical valve body having aneck portion at the upper part of the valve body, a cone-shaped valveseat at the lower end of the valve body, and a cylindrical sternslidable within the valve body, whereby c. the central portion of thevalve stem is in sliding contact with the neck portion of the valve bodyand the upper and lower portions of the valve body are spaced from thevalve stem to define an upper annular chamber above the neck portion anda lower annular chamber below the neck portion,

. the lower chamber is connected into the outlet end of the transferline and is adapted to receive a molten liquid from the transfer line,

. a packing material is positioned in the upper chamber to provide aliquid-tight seal between the valve stem and valve body,

f. the valve stem further includes a hemispherical lower end adapted tosealingly engage the coneshaped valve seat, a central bore which extendslengthwise through the valve stem, an inlet channel in communicationwith the upper end of the stem bore, for directing a fluid material intothe bore, and several outlet channels which connect the lower end of thestem bore with the lower end of the valve stem, for discharging thefluid material into the valve seat,

. the upper end of the valve stem is connected by a coupling member to apower means adapted to move the valve stem up and down in the valvebody, and

. the transfer line and valve body are connected by an electricalcircuit into a source of electrical power, to thereby heat the transferline and valve assembly.

2. The apparatus of claim 1 which includes a second electrical circuitconnecting the valve stem with a source of electrical power.

The apparatus of claim 1 in which the molten

1. In an apparatus for transferring a molten liquid from one point toanother, the combination which includes: a. a transfer line forconducting the molten liquid, including a valve assembly connected tothe outlet end of the transfer line, b. the valve assembly being definedby a cylindrical valve body having a neck portion at the upper part ofthe valve body, a cone-shaped valve seat at the lower end of the valvebody, and a cylindrical stem slidable within the valve body, whereby c.the central portion of the valve stem is in sliding contact with theneck portion of the valve body and the upper and lower portions of thevalve body are spaced from the valve stem to define an upper annularchamber above the neck portion and a lower annular chamber below theneck portion, d. the lower chamber is connected into the outlet end ofthe transfer line and is adapted to receive a molten liquid from thetransfer line, e. a packing material is positioned in the upper chamberto provide a liquid-tight seal between the valve stem anD valve body, f.the valve stem further includes a hemispherical lower end adapted tosealingly engage the cone-shaped valve seat, a central bore whichextends lengthwise through the valve stem, an inlet channel incommunication with the upper end of the stem bore, for directing a fluidmaterial into the bore, and several outlet channels which connect thelower end of the stem bore with the lower end of the valve stem, fordischarging the fluid material into the valve seat, g. the upper end ofthe valve stem is connected by a coupling member to a power meansadapted to move the valve stem up and down in the valve body, and h. thetransfer line and valve body are connected by an electrical circuit intoa source of electrical power, to thereby heat the transfer line andvalve assembly.
 2. The apparatus of claim 1 which includes a secondelectrical circuit connecting the valve stem with a source of electricalpower.
 3. The apparatus of claim 1 in which the molten liquid beingtransferred is a magnesium alloy or a zinc alloy.
 4. The apparatus ofclaim 1 in which the fluid material directed into the valve stem bore isa protective gas.
 5. The apparatus of claim 1 in which the packingmaterial is graphite.